mss1: move code that will be reused by MSS2 decoder into separate file

4 files changed, 691 insertions, 596 deletions

diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 394966e2fd..87f716ce36 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -270,7 +270,7 @@ OBJS-$(CONFIG_MSMPEG4V3_ENCODER)       += msmpeg4.o msmpeg4enc.o msmpeg4data.o \
                                           mpeg4videodec.o
 OBJS-$(CONFIG_MSRLE_DECODER)           += msrle.o msrledec.o
 OBJS-$(CONFIG_MSA1_DECODER)            += mss3.o mss34dsp.o
-OBJS-$(CONFIG_MSS1_DECODER)            += mss1.o
+OBJS-$(CONFIG_MSS1_DECODER)            += mss1.o mss12.o
 OBJS-$(CONFIG_MSVIDEO1_DECODER)        += msvideo1.o
 OBJS-$(CONFIG_MSZH_DECODER)            += lcldec.o
 OBJS-$(CONFIG_MTS2_DECODER)            += mss4.o mss34dsp.o
diff --git a/libavcodec/mss1.c b/libavcodec/mss1.c
index 4cd828d977..fe8ee10840 100644
--- a/libavcodec/mss1.c
+++ b/libavcodec/mss1.c
@@ -27,74 +27,13 @@
 #include "libavutil/intfloat.h"
 #include "libavutil/intreadwrite.h"
 #include "avcodec.h"
-#include "get_bits.h"
-
-enum SplitMode {
-    SPLIT_VERT = 0,
-    SPLIT_HOR,
-    SPLIT_NONE
-};
-
-typedef struct ArithCoder {
-    int low, high, value;
-    GetBitContext *gb;
-} ArithCoder;
-
-#define MODEL_MIN_SYMS    2
-#define MODEL_MAX_SYMS  256
-#define THRESH_ADAPTIVE  -1
-#define THRESH_LOW       15
-#define THRESH_HIGH      50
-
-typedef struct Model {
-    int cum_prob[MODEL_MAX_SYMS + 1];
-    int weights[MODEL_MAX_SYMS + 1];
-    int idx2sym[MODEL_MAX_SYMS + 1];
-    int sym2idx[MODEL_MAX_SYMS + 1];
-    int num_syms;
-    int thr_weight, threshold;
-} Model;
-
-static const int sec_order_sizes[4] = { 1, 7, 6, 1 };
-
-enum ContextDirection {
-    TOP_LEFT = 0,
-    TOP,
-    TOP_RIGHT,
-    LEFT
-};
-
-typedef struct PixContext {
-    int cache_size, num_syms;
-    uint8_t cache[12];
-    Model cache_model, full_model;
-    Model sec_models[4][8][4];
-} PixContext;
+#include "mss12.h"
 
 typedef struct MSS1Context {
-    AVCodecContext *avctx;
+    MSS12Context   ctx;
     AVFrame        pic;
-    uint8_t        *pic_start;
-    int            pic_stride;
-    uint8_t        *mask;
-    int            mask_linesize;
-    uint32_t       pal[256];
-    int            free_colours;
-    int            keyframe;
-    Model          intra_region, inter_region;
-    Model          pivot, edge_mode, split_mode;
-    PixContext     intra_pix_ctx, inter_pix_ctx;
-    int            corrupted;
 } MSS1Context;
 
-static void arith_init(ArithCoder *c, GetBitContext *gb)
-{
-    c->low   = 0;
-    c->high  = 0xFFFF;
-    c->value = get_bits(gb, 16);
-    c->gb    = gb;
-}
-
 static void arith_normalise(ArithCoder *c)
 {
     for (;;) {
@@ -179,88 +118,6 @@ static int arith_get_prob(ArithCoder *c, int *probs)
     return sym;
 }
 
-static int model_calc_threshold(Model *m)
-{
-    int thr;
-
-    if (m->thr_weight == -1) {
-        thr = 2 * m->weights[m->num_syms] - 1;
-        thr = ((thr >> 1) + 4 * m->cum_prob[0]) / thr;
-    } else {
-        thr = m->num_syms * m->thr_weight;
-    }
-
-    return FFMIN(thr, 0x3FFF);
-}
-
-static void model_reset(Model *m)
-{
-    int i;
-
-    for (i = 0; i <= m->num_syms; i++) {
-        m->weights[i]  = 1;
-        m->cum_prob[i] = m->num_syms - i;
-    }
-    m->weights[0]           = -1;
-    m->idx2sym[0]           = -1;
-    m->sym2idx[m->num_syms] = -1;
-    for (i = 0; i < m->num_syms; i++) {
-        m->sym2idx[i]     = i + 1;
-        m->idx2sym[i + 1] = i;
-    }
-}
-
-static av_cold void model_init(Model *m, int num_syms, int thr_weight)
-{
-    m->num_syms   = num_syms;
-    m->thr_weight = thr_weight;
-    m->threshold  = model_calc_threshold(m);
-    model_reset(m);
-}
-
-static void model_rescale_weights(Model *m)
-{
-    int i;
-    int cum_prob;
-
-    if (m->thr_weight == -1)
-        m->threshold = model_calc_threshold(m);
-    while (m->cum_prob[0] > m->threshold) {
-        cum_prob = 0;
-        for (i = m->num_syms; i >= 0; i--) {
-            m->cum_prob[i] = cum_prob;
-            m->weights[i]  = (m->weights[i] + 1) >> 1;
-            cum_prob      += m->weights[i];
-        }
-    }
-}
-
-static void model_update(Model *m, int val)
-{
-    int i;
-
-    if (m->weights[val] == m->weights[val - 1]) {
-        for (i = val; m->weights[i - 1] == m->weights[val]; i--);
-        if (i != val) {
-            int sym1, sym2;
-
-            sym1 = m->idx2sym[val];
-            sym2 = m->idx2sym[i];
-
-            m->idx2sym[val]  = sym2;
-            m->idx2sym[i]    = sym1;
-            m->sym2idx[sym1] = i;
-            m->sym2idx[sym2] = val;
-
-            val = i;
-        }
-    }
-    m->weights[val]++;
-    for (i = val - 1; i >= 0; i--)
-        m->cum_prob[i]++;
-    model_rescale_weights(m);
-}
-
 static int arith_get_model_sym(ArithCoder *c, Model *m)
 {
     int idx, val;
@@ -268,289 +125,33 @@ static int arith_get_model_sym(ArithCoder *c, Model *m)
     idx = arith_get_prob(c, m->cum_prob);
 
     val = m->idx2sym[idx];
-    model_update(m, idx);
+    ff_mss12_model_update(m, idx);
 
     arith_normalise(c);
 
     return val;
 }
 
-static void pixctx_reset(PixContext *ctx)
-{
-    int i, j, k;
-
-    for (i = 0; i < ctx->cache_size; i++)
-        ctx->cache[i] = i;
-
-    model_reset(&ctx->cache_model);
-    model_reset(&ctx->full_model);
-
-    for (i = 0; i < 4; i++)
-        for (j = 0; j < sec_order_sizes[i]; j++)
-            for (k = 0; k < 4; k++)
-                model_reset(&ctx->sec_models[i][j][k]);
-}
-
-static av_cold void pixctx_init(PixContext *ctx, int cache_size)
-{
-    int i, j, k;
-
-    ctx->cache_size = cache_size + 4;
-    ctx->num_syms   = cache_size;
-
-    for (i = 0; i < ctx->cache_size; i++)
-        ctx->cache[i] = i;
-
-    model_init(&ctx->cache_model, ctx->num_syms + 1, THRESH_LOW);
-    model_init(&ctx->full_model, 256, THRESH_HIGH);
-
-    for (i = 0; i < 4; i++) {
-        for (j = 0; j < sec_order_sizes[i]; j++) {
-            for (k = 0; k < 4; k++) {
-                model_init(&ctx->sec_models[i][j][k], 2 + i,
-                           i ? THRESH_LOW : THRESH_ADAPTIVE);
-            }
-        }
-    }
-}
-
-static int decode_top_left_pixel(ArithCoder *acoder, PixContext *pctx)
-{
-    int i, val, pix;
-
-    val = arith_get_model_sym(acoder, &pctx->cache_model);
-    if (val < pctx->num_syms) {
-        pix = pctx->cache[val];
-    } else {
-        pix = arith_get_model_sym(acoder, &pctx->full_model);
-        for (i = 0; i < pctx->cache_size - 1; i++)
-            if (pctx->cache[i] == pix)
-                break;
-        val = i;
-    }
-    if (val) {
-        for (i = val; i > 0; i--)
-            pctx->cache[i] = pctx->cache[i - 1];
-        pctx->cache[0] = pix;
-    }
-
-    return pix;
-}
-
-static int decode_pixel(ArithCoder *acoder, PixContext *pctx,
-                        uint8_t *ngb, int num_ngb)
-{
-    int i, val, pix;
-
-    val = arith_get_model_sym(acoder, &pctx->cache_model);
-    if (val < pctx->num_syms) {
-        int idx, j;
-
-
-        idx = 0;
-        for (i = 0; i < pctx->cache_size; i++) {
-            for (j = 0; j < num_ngb; j++)
-                if (pctx->cache[i] == ngb[j])
-                    break;
-            if (j == num_ngb) {
-                if (idx == val)
-                    break;
-                idx++;
-            }
-        }
-        val = FFMIN(i, pctx->cache_size - 1);
-        pix = pctx->cache[val];
-    } else {
-        pix = arith_get_model_sym(acoder, &pctx->full_model);
-        for (i = 0; i < pctx->cache_size - 1; i++)
-            if (pctx->cache[i] == pix)
-                break;
-        val = i;
-    }
-    if (val) {
-        for (i = val; i > 0; i--)
-            pctx->cache[i] = pctx->cache[i - 1];
-        pctx->cache[0] = pix;
-    }
-
-    return pix;
-}
-
-static int decode_pixel_in_context(ArithCoder *acoder, PixContext *pctx,
-                                   uint8_t *src, int stride, int x, int y,
-                                   int has_right)
-{
-    uint8_t neighbours[4];
-    uint8_t ref_pix[4];
-    int nlen;
-    int layer = 0, sub;
-    int pix;
-    int i, j;
-
-    if (!y) {
-        memset(neighbours, src[-1], 4);
-    } else {
-        neighbours[TOP] = src[-stride];
-        if (!x) {
-            neighbours[TOP_LEFT] = neighbours[LEFT] = neighbours[TOP];
-        } else {
-            neighbours[TOP_LEFT] = src[-stride - 1];
-            neighbours[    LEFT] = src[-1];
-        }
-        if (has_right)
-            neighbours[TOP_RIGHT] = src[-stride + 1];
-        else
-            neighbours[TOP_RIGHT] = neighbours[TOP];
-    }
-
-    sub = 0;
-    if (x >= 2 && src[-2] == neighbours[LEFT])
-        sub  = 1;
-    if (y >= 2 && src[-2 * stride] == neighbours[TOP])
-        sub |= 2;
-
-    nlen = 1;
-    ref_pix[0] = neighbours[0];
-    for (i = 1; i < 4; i++) {
-        for (j = 0; j < nlen; j++)
-            if (ref_pix[j] == neighbours[i])
-                break;
-        if (j == nlen)
-            ref_pix[nlen++] = neighbours[i];
-    }
-
-    switch (nlen) {
-    case 1:
-    case 4:
-        layer = 0;
-        break;
-    case 2:
-        if (neighbours[TOP] == neighbours[TOP_LEFT]) {
-            if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT])
-                layer = 3;
-            else if (neighbours[LEFT] == neighbours[TOP_LEFT])
-                layer = 2;
-            else
-                layer = 4;
-        } else if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT]) {
-            if (neighbours[LEFT] == neighbours[TOP_LEFT])
-                layer = 1;
-            else
-                layer = 5;
-        } else if (neighbours[LEFT] == neighbours[TOP_LEFT]) {
-            layer = 6;
-        } else {
-            layer = 0;
-        }
-        break;
-    case 3:
-        if (neighbours[TOP] == neighbours[TOP_LEFT])
-            layer = 0;
-        else if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT])
-            layer = 1;
-        else if (neighbours[LEFT] == neighbours[TOP_LEFT])
-            layer = 2;
-        else if (neighbours[TOP_RIGHT] == neighbours[TOP])
-            layer = 3;
-        else if (neighbours[TOP] == neighbours[LEFT])
-            layer = 4;
-        else
-            layer = 5;
-        break;
-    }
-
-    pix = arith_get_model_sym(acoder, &pctx->sec_models[nlen - 1][layer][sub]);
-    if (pix < nlen)
-        return ref_pix[pix];
-    else
-        return decode_pixel(acoder, pctx, ref_pix, nlen);
-}
-
-static int decode_region(MSS1Context *ctx, ArithCoder *acoder, uint8_t *dst,
-                         int x, int y, int width, int height, int stride,
-                         PixContext *pctx)
-{
-    int i, j;
-
-    dst += x + y * stride;
-
-    dst[0] = decode_top_left_pixel(acoder, pctx);
-    for (j = 0; j < height; j++) {
-        for (i = 0; i < width; i++) {
-            if (!i && !j)
-                continue;
-
-            dst[i] = decode_pixel_in_context(acoder, pctx, dst + i, stride,
-                                             i, j, width - i - 1);
-        }
-        dst += stride;
-    }
-
-    return 0;
-}
-
-static int decode_region_masked(MSS1Context *ctx, ArithCoder *acoder,
-                                uint8_t *dst, int stride, uint8_t *mask,
-                                int mask_stride, int x, int y,
-                                int width, int height,
-                                PixContext *pctx)
-{
-    int i, j;
-
-    dst  += x + y * stride;
-    mask += x + y * mask_stride;
-
-    if (mask[0] == 0xFF)
-        dst[0] = decode_top_left_pixel(acoder, pctx);
-    for (j = 0; j < height; j++) {
-        for (i = 0; i < width; i++) {
-            if (!i && !j || mask[i] != 0xFF)
-                continue;
-
-            dst[i] = decode_pixel_in_context(acoder, pctx, dst + i, stride,
-                                             i, j, width - i - 1);
-        }
-        dst  += stride;
-        mask += mask_stride;
-    }
-
-    return 0;
-}
-
-static av_cold void codec_init(MSS1Context *ctx)
+static void arith_init(ArithCoder *c, GetBitContext *gb)
 {
-    model_init(&ctx->intra_region, 2, THRESH_ADAPTIVE);
-    model_init(&ctx->inter_region, 2, THRESH_ADAPTIVE);
-    model_init(&ctx->split_mode,   3, THRESH_HIGH);
-    model_init(&ctx->edge_mode,    2, THRESH_HIGH);
-    model_init(&ctx->pivot,        3, THRESH_LOW);
-    pixctx_init(&ctx->intra_pix_ctx, 8);
-    pixctx_init(&ctx->inter_pix_ctx, 2);
-    ctx->corrupted = 1;
-}
+    c->low   = 0;
+    c->high  = 0xFFFF;
+    c->value = get_bits(gb, 16);
+    c->gb    = gb;
 
-static void codec_reset(MSS1Context *ctx)
-{
-    model_reset(&ctx->intra_region);
-    model_reset(&ctx->inter_region);
-    model_reset(&ctx->split_mode);
-    model_reset(&ctx->edge_mode);
-    model_reset(&ctx->pivot);
-    pixctx_reset(&ctx->intra_pix_ctx);
-    pixctx_reset(&ctx->inter_pix_ctx);
-
-    ctx->corrupted = 0;
+    c->get_model_sym = arith_get_model_sym;
+    c->get_number    = arith_get_number;
 }
 
 static int decode_pal(MSS1Context *ctx, ArithCoder *acoder)
 {
     int i, ncol, r, g, b;
-    uint32_t *pal = ctx->pal + 256 - ctx->free_colours;
+    uint32_t *pal = ctx->ctx.pal + 256 - ctx->ctx.free_colours;
 
-    if (!ctx->free_colours)
+    if (!ctx->ctx.free_colours)
         return 0;
 
-    ncol = arith_get_number(acoder, ctx->free_colours + 1);
+    ncol = arith_get_number(acoder, ctx->ctx.free_colours + 1);
     for (i = 0; i < ncol; i++) {
         r = arith_get_bits(acoder, 8);
         g = arith_get_bits(acoder, 8);
@@ -561,119 +162,6 @@ static int decode_pal(MSS1Context *ctx, ArithCoder *acoder)
     return !!ncol;
 }
 
-static int decode_pivot(MSS1Context *ctx, ArithCoder *acoder, int base)
-{
-    int val, inv;
-
-    inv = arith_get_model_sym(acoder, &ctx->edge_mode);
-    val = arith_get_model_sym(acoder, &ctx->pivot) + 1;
-
-    if (val > 2) {
-        if ((base + 1) / 2 - 2 <= 0) {
-            ctx->corrupted = 1;
-            return 0;
-        }
-        val = arith_get_number(acoder, (base + 1) / 2 - 2) + 3;
-    }
-
-    if (val == base) {
-        ctx->corrupted = 1;
-        return 0;
-    }
-
-    return inv ? base - val : val;
-}
-
-static int decode_region_intra(MSS1Context *ctx, ArithCoder *acoder,
-                               int x, int y, int width, int height)
-{
-    int mode;
-
-    mode = arith_get_model_sym(acoder, &ctx->intra_region);
-
-    if (!mode) {
-        int i, pix;
-        int stride = ctx->pic_stride;
-        uint8_t *dst = ctx->pic_start + x + y * stride;
-
-        pix = decode_top_left_pixel(acoder, &ctx->intra_pix_ctx);
-        for (i = 0; i < height; i++, dst += stride)
-            memset(dst, pix, width);
-    } else {
-        return decode_region(ctx, acoder, ctx->pic_start,
-                             x, y, width, height, ctx->pic_stride,
-                             &ctx->intra_pix_ctx);
-    }
-
-    return 0;
-}
-
-static int decode_region_inter(MSS1Context *ctx, ArithCoder *acoder,
-                               int x, int y, int width, int height)
-{
-    int mode;
-
-    mode = arith_get_model_sym(acoder, &ctx->inter_region);
-
-    if (!mode) {
-        mode = decode_top_left_pixel(acoder, &ctx->inter_pix_ctx);
-        if (mode != 0xFF) {
-            return 0;
-        } else {
-            return decode_region_intra(ctx, acoder, x, y, width, height);
-        }
-    } else {
-        if (decode_region(ctx, acoder, ctx->mask,
-                          x, y, width, height, ctx->mask_linesize,
-                          &ctx->inter_pix_ctx) < 0)
-            return -1;
-        return decode_region_masked(ctx, acoder, ctx->pic_start,
-                                    -ctx->pic.linesize[0], ctx->mask,
-                                    ctx->mask_linesize,
-                                    x, y, width, height,
-                                    &ctx->intra_pix_ctx);
-    }
-
-    return 0;
-}
-
-static int decode_rect(MSS1Context *ctx, ArithCoder *acoder,
-                       int x, int y, int width, int height)
-{
-    int mode, pivot;
-
-    if (ctx->corrupted)
-        return -1;
-
-    mode = arith_get_model_sym(acoder, &ctx->split_mode);
-
-    switch (mode) {
-    case SPLIT_VERT:
-        pivot = decode_pivot(ctx, acoder, height);
-        if (decode_rect(ctx, acoder, x, y, width, pivot))
-            return -1;
-        if (decode_rect(ctx, acoder, x, y + pivot, width, height - pivot))
-            return -1;
-        break;
-    case SPLIT_HOR:
-        pivot = decode_pivot(ctx, acoder, width);
-        if (decode_rect(ctx, acoder, x, y, pivot, height))
-            return -1;
-        if (decode_rect(ctx, acoder, x + pivot, y, width - pivot, height))
-            return -1;
-        break;
-    case SPLIT_NONE:
-        if (ctx->keyframe)
-            return decode_region_intra(ctx, acoder, x, y, width, height);
-        else
-            return decode_region_inter(ctx, acoder, x, y, width, height);
-    default:
-        return -1;
-    }
-
-    return 0;
-}
-
 static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
                              AVPacket *avpkt)
 {
@@ -696,24 +184,25 @@ static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
         return ret;
     }
 
-    c->pic_start  = c->pic.data[0] + c->pic.linesize[0] * (avctx->height - 1);
-    c->pic_stride = -c->pic.linesize[0];
-    c->keyframe   = !arith_get_bit(&acoder);
-    if (c->keyframe) {
-        codec_reset(c);
+    c->ctx.pic_start  = c->pic.data[0] + c->pic.linesize[0] * (avctx->height - 1);
+    c->ctx.pic_stride = -c->pic.linesize[0];
+    c->ctx.keyframe   = !arith_get_bit(&acoder);
+    if (c->ctx.keyframe) {
+        ff_mss12_codec_reset(&c->ctx);
         pal_changed      = decode_pal(c, &acoder);
         c->pic.key_frame = 1;
         c->pic.pict_type = AV_PICTURE_TYPE_I;
     } else {
-        if (c->corrupted)
+        if (c->ctx.corrupted)
             return AVERROR_INVALIDDATA;
         c->pic.key_frame = 0;
         c->pic.pict_type = AV_PICTURE_TYPE_P;
     }
-    c->corrupted = decode_rect(c, &acoder, 0, 0, avctx->width, avctx->height);
-    if (c->corrupted)
+    c->ctx.corrupted = ff_mss12_decode_rect(&c->ctx, &acoder, 0, 0,
+                                            avctx->width, avctx->height);
+    if (c->ctx.corrupted)
         return AVERROR_INVALIDDATA;
-    memcpy(c->pic.data[1], c->pal, AVPALETTE_SIZE);
+    memcpy(c->pic.data[1], c->ctx.pal, AVPALETTE_SIZE);
     c->pic.palette_has_changed = pal_changed;
 
     *data_size = sizeof(AVFrame);
@@ -726,69 +215,11 @@ static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *data_size,
 static av_cold int mss1_decode_init(AVCodecContext *avctx)
 {
     MSS1Context * const c = avctx->priv_data;
-    int i;
-
-    c->avctx = avctx;
-
-    if (avctx->extradata_size < 52 + 256 * 3) {
-        av_log(avctx, AV_LOG_ERROR, "Insufficient extradata size %d\n",
-               avctx->extradata_size);
-        return AVERROR_INVALIDDATA;
-    }
-
-    if (AV_RB32(avctx->extradata) < avctx->extradata_size) {
-        av_log(avctx, AV_LOG_ERROR,
-               "Insufficient extradata size: expected %d got %d\n",
-               AV_RB32(avctx->extradata),
-               avctx->extradata_size);
-        return AVERROR_INVALIDDATA;
-    }
-
-    av_log(avctx, AV_LOG_DEBUG, "Encoder version %d.%d\n",
-           AV_RB32(avctx->extradata + 4), AV_RB32(avctx->extradata + 8));
-    c->free_colours     = AV_RB32(avctx->extradata + 48);
-    if ((unsigned)c->free_colours > 256) {
-        av_log(avctx, AV_LOG_ERROR,
-               "Incorrect number of changeable palette entries: %d\n",
-               c->free_colours);
-        return AVERROR_INVALIDDATA;
-    }
-    av_log(avctx, AV_LOG_DEBUG, "%d free colour(s)\n", c->free_colours);
-    avctx->coded_width  = AV_RB32(avctx->extradata + 20);
-    avctx->coded_height = AV_RB32(avctx->extradata + 24);
-
-    av_log(avctx, AV_LOG_DEBUG, "Display dimensions %dx%d\n",
-           AV_RB32(avctx->extradata + 12), AV_RB32(avctx->extradata + 16));
-    av_log(avctx, AV_LOG_DEBUG, "Coded dimensions %dx%d\n",
-           avctx->coded_width, avctx->coded_height);
-    av_log(avctx, AV_LOG_DEBUG, "%g frames per second\n",
-           av_int2float(AV_RB32(avctx->extradata + 28)));
-    av_log(avctx, AV_LOG_DEBUG, "Bitrate %d bps\n",
-           AV_RB32(avctx->extradata + 32));
-    av_log(avctx, AV_LOG_DEBUG, "Max. lead time %g ms\n",
-           av_int2float(AV_RB32(avctx->extradata + 36)));
-    av_log(avctx, AV_LOG_DEBUG, "Max. lag time %g ms\n",
-           av_int2float(AV_RB32(avctx->extradata + 40)));
-    av_log(avctx, AV_LOG_DEBUG, "Max. seek time %g ms\n",
-           av_int2float(AV_RB32(avctx->extradata + 44)));
-
-    for (i = 0; i < 256; i++)
-        c->pal[i] = AV_RB24(avctx->extradata + 52 + i * 3);
-
-    avctx->pix_fmt = PIX_FMT_PAL8;
-
-    c->mask_linesize = FFALIGN(avctx->width, 16);
-    c->mask          = av_malloc(c->mask_linesize * avctx->height);
-    if (!c->mask) {
-        av_log(avctx, AV_LOG_ERROR, "Cannot allocate mask plane\n");
-        return AVERROR(ENOMEM);
-    }
 
+    c->ctx.avctx       = avctx;
     avctx->coded_frame = &c->pic;
 
-    codec_init(c);
-
-    return 0;
+    return ff_mss12_decode_init(avctx, 0);
 }
 
 static av_cold int mss1_decode_end(AVCodecContext *avctx)
@@ -797,7 +228,7 @@ static av_cold int mss1_decode_end(AVCodecContext *avctx)
 
     if (c->pic.data[0])
         avctx->release_buffer(avctx, &c->pic);
-    av_freep(&c->mask);
+    ff_mss12_decode_end(avctx);
 
     return 0;
 }
diff --git a/libavcodec/mss12.c b/libavcodec/mss12.c
new file mode 100644
index 0000000000..8b4f52bf5f
--- /dev/null
+++ b/libavcodec/mss12.c
@@ -0,0 +1,581 @@
+/*
+ * Copyright (c) 2012 Konstantin Shishkov
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * Common functions for Microsoft Screen 1 and 2
+ */
+
+#include "libavutil/intfloat.h"
+#include "libavutil/intreadwrite.h"
+#include "avcodec.h"
+#include "mss12.h"
+
+enum SplitMode {
+    SPLIT_VERT = 0,
+    SPLIT_HOR,
+    SPLIT_NONE
+};
+
+static const int sec_order_sizes[4] = { 1, 7, 6, 1 };
+
+enum ContextDirection {
+    TOP_LEFT = 0,
+    TOP,
+    TOP_RIGHT,
+    LEFT
+};
+
+static int model_calc_threshold(Model *m)
+{
+    int thr;
+
+    if (m->thr_weight == -1) {
+        thr = 2 * m->weights[m->num_syms] - 1;
+        thr = ((thr >> 1) + 4 * m->cum_prob[0]) / thr;
+    } else {
+        thr = m->num_syms * m->thr_weight;
+    }
+
+    return FFMIN(thr, 0x3FFF);
+}
+
+static void model_reset(Model *m)
+{
+    int i;
+
+    for (i = 0; i <= m->num_syms; i++) {
+        m->weights[i]  = 1;
+        m->cum_prob[i] = m->num_syms - i;
+    }
+    m->weights[0]           = -1;
+    m->idx2sym[0]           = -1;
+    m->sym2idx[m->num_syms] = -1;
+    for (i = 0; i < m->num_syms; i++) {
+        m->sym2idx[i]     = i + 1;
+        m->idx2sym[i + 1] = i;
+    }
+}
+
+static av_cold void model_init(Model *m, int num_syms, int thr_weight)
+{
+    m->num_syms   = num_syms;
+    m->thr_weight = thr_weight;
+    m->threshold  = model_calc_threshold(m);
+    model_reset(m);
+}
+
+static void model_rescale_weights(Model *m)
+{
+    int i;
+    int cum_prob;
+
+    if (m->thr_weight == -1)
+        m->threshold = model_calc_threshold(m);
+    while (m->cum_prob[0] > m->threshold) {
+        cum_prob = 0;
+        for (i = m->num_syms; i >= 0; i--) {
+            m->cum_prob[i] = cum_prob;
+            m->weights[i]  = (m->weights[i] + 1) >> 1;
+            cum_prob      += m->weights[i];
+        }
+    }
+}
+
+void ff_mss12_model_update(Model *m, int val)
+{
+    int i;
+
+    if (m->weights[val] == m->weights[val - 1]) {
+        for (i = val; m->weights[i - 1] == m->weights[val]; i--);
+        if (i != val) {
+            int sym1, sym2;
+
+            sym1 = m->idx2sym[val];
+            sym2 = m->idx2sym[i];
+
+            m->idx2sym[val]  = sym2;
+            m->idx2sym[i]    = sym1;
+            m->sym2idx[sym1] = i;
+            m->sym2idx[sym2] = val;
+
+            val = i;
+        }
+    }
+    m->weights[val]++;
+    for (i = val - 1; i >= 0; i--)
+        m->cum_prob[i]++;
+    model_rescale_weights(m);
+}
+
+static void pixctx_reset(PixContext *ctx)
+{
+    int i, j, k;
+
+    for (i = 0; i < ctx->cache_size; i++)
+        ctx->cache[i] = i;
+
+    model_reset(&ctx->cache_model);
+    model_reset(&ctx->full_model);
+
+    for (i = 0; i < 4; i++)
+        for (j = 0; j < sec_order_sizes[i]; j++)
+            for (k = 0; k < 4; k++)
+                model_reset(&ctx->sec_models[i][j][k]);
+}
+
+static av_cold void pixctx_init(PixContext *ctx, int cache_size)
+{
+    int i, j, k;
+
+    ctx->cache_size = cache_size + 4;
+    ctx->num_syms   = cache_size;
+
+    for (i = 0; i < ctx->cache_size; i++)
+        ctx->cache[i] = i;
+
+    model_init(&ctx->cache_model, ctx->num_syms + 1, THRESH_LOW);
+    model_init(&ctx->full_model, 256, THRESH_HIGH);
+
+    for (i = 0; i < 4; i++) {
+        for (j = 0; j < sec_order_sizes[i]; j++) {
+            for (k = 0; k < 4; k++) {
+                model_init(&ctx->sec_models[i][j][k], 2 + i,
+                           i ? THRESH_LOW : THRESH_ADAPTIVE);
+            }
+        }
+    }
+}
+
+static int decode_top_left_pixel(ArithCoder *acoder, PixContext *pctx)
+{
+    int i, val, pix;
+
+    val = acoder->get_model_sym(acoder, &pctx->cache_model);
+    if (val < pctx->num_syms) {
+        pix = pctx->cache[val];
+    } else {
+        pix = acoder->get_model_sym(acoder, &pctx->full_model);
+        for (i = 0; i < pctx->cache_size - 1; i++)
+            if (pctx->cache[i] == pix)
+                break;
+        val = i;
+    }
+    if (val) {
+        for (i = val; i > 0; i--)
+            pctx->cache[i] = pctx->cache[i - 1];
+        pctx->cache[0] = pix;
+    }
+
+    return pix;
+}
+
+static int decode_pixel(ArithCoder *acoder, PixContext *pctx,
+                        uint8_t *ngb, int num_ngb)
+{
+    int i, val, pix;
+
+    val = acoder->get_model_sym(acoder, &pctx->cache_model);
+    if (val < pctx->num_syms) {
+        int idx, j;
+
+
+        idx = 0;
+        for (i = 0; i < pctx->cache_size; i++) {
+            for (j = 0; j < num_ngb; j++)
+                if (pctx->cache[i] == ngb[j])
+                    break;
+            if (j == num_ngb) {
+                if (idx == val)
+                    break;
+                idx++;
+            }
+        }
+        val = FFMIN(i, pctx->cache_size - 1);
+        pix = pctx->cache[val];
+    } else {
+        pix = acoder->get_model_sym(acoder, &pctx->full_model);
+        for (i = 0; i < pctx->cache_size - 1; i++)
+            if (pctx->cache[i] == pix)
+                break;
+        val = i;
+    }
+    if (val) {
+        for (i = val; i > 0; i--)
+            pctx->cache[i] = pctx->cache[i - 1];
+        pctx->cache[0] = pix;
+    }
+
+    return pix;
+}
+
+static int decode_pixel_in_context(ArithCoder *acoder, PixContext *pctx,
+                                   uint8_t *src, int stride, int x, int y,
+                                   int has_right)
+{
+    uint8_t neighbours[4];
+    uint8_t ref_pix[4];
+    int nlen;
+    int layer = 0, sub;
+    int pix;
+    int i, j;
+
+    if (!y) {
+        memset(neighbours, src[-1], 4);
+    } else {
+        neighbours[TOP] = src[-stride];
+        if (!x) {
+            neighbours[TOP_LEFT] = neighbours[LEFT] = neighbours[TOP];
+        } else {
+            neighbours[TOP_LEFT] = src[-stride - 1];
+            neighbours[    LEFT] = src[-1];
+        }
+        if (has_right)
+            neighbours[TOP_RIGHT] = src[-stride + 1];
+        else
+            neighbours[TOP_RIGHT] = neighbours[TOP];
+    }
+
+    sub = 0;
+    if (x >= 2 && src[-2] == neighbours[LEFT])
+        sub  = 1;
+    if (y >= 2 && src[-2 * stride] == neighbours[TOP])
+        sub |= 2;
+
+    nlen = 1;
+    ref_pix[0] = neighbours[0];
+    for (i = 1; i < 4; i++) {
+        for (j = 0; j < nlen; j++)
+            if (ref_pix[j] == neighbours[i])
+                break;
+        if (j == nlen)
+            ref_pix[nlen++] = neighbours[i];
+    }
+
+    switch (nlen) {
+    case 1:
+    case 4:
+        layer = 0;
+        break;
+    case 2:
+        if (neighbours[TOP] == neighbours[TOP_LEFT]) {
+            if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT])
+                layer = 3;
+            else if (neighbours[LEFT] == neighbours[TOP_LEFT])
+                layer = 2;
+            else
+                layer = 4;
+        } else if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT]) {
+            if (neighbours[LEFT] == neighbours[TOP_LEFT])
+                layer = 1;
+            else
+                layer = 5;
+        } else if (neighbours[LEFT] == neighbours[TOP_LEFT]) {
+            layer = 6;
+        } else {
+            layer = 0;
+        }
+        break;
+    case 3:
+        if (neighbours[TOP] == neighbours[TOP_LEFT])
+            layer = 0;
+        else if (neighbours[TOP_RIGHT] == neighbours[TOP_LEFT])
+            layer = 1;
+        else if (neighbours[LEFT] == neighbours[TOP_LEFT])
+            layer = 2;
+        else if (neighbours[TOP_RIGHT] == neighbours[TOP])
+            layer = 3;
+        else if (neighbours[TOP] == neighbours[LEFT])
+            layer = 4;
+        else
+            layer = 5;
+        break;
+    }
+
+    pix = acoder->get_model_sym(acoder, &pctx->sec_models[nlen - 1][layer][sub]);
+    if (pix < nlen)
+        return ref_pix[pix];
+    else
+        return decode_pixel(acoder, pctx, ref_pix, nlen);
+}
+
+static int decode_region(MSS12Context *ctx, ArithCoder *acoder, uint8_t *dst,
+                         int x, int y, int width, int height, int stride,
+                         PixContext *pctx)
+{
+    int i, j;
+
+    dst += x + y * stride;
+
+    dst[0] = decode_top_left_pixel(acoder, pctx);
+    for (j = 0; j < height; j++) {
+        for (i = 0; i < width; i++) {
+            if (!i && !j)
+                continue;
+
+            dst[i] = decode_pixel_in_context(acoder, pctx, dst + i, stride,
+                                             i, j, width - i - 1);
+        }
+        dst += stride;
+    }
+
+    return 0;
+}
+
+static int decode_region_masked(MSS12Context *ctx, ArithCoder *acoder,
+                                uint8_t *dst, int stride, uint8_t *mask,
+                                int mask_stride, int x, int y,
+                                int width, int height,
+                                PixContext *pctx)
+{
+    int i, j;
+
+    dst  += x + y * stride;
+    mask += x + y * mask_stride;
+
+    if (mask[0] == 0xFF)
+        dst[0] = decode_top_left_pixel(acoder, pctx);
+    for (j = 0; j < height; j++) {
+        for (i = 0; i < width; i++) {
+            if (!i && !j || mask[i] != 0xFF)
+                continue;
+
+            dst[i] = decode_pixel_in_context(acoder, pctx, dst + i, stride,
+                                             i, j, width - i - 1);
+        }
+        dst  += stride;
+        mask += mask_stride;
+    }
+
+    return 0;
+}
+
+static av_cold void codec_init(MSS12Context *ctx)
+{
+    model_init(&ctx->intra_region, 2, THRESH_ADAPTIVE);
+    model_init(&ctx->inter_region, 2, THRESH_ADAPTIVE);
+    model_init(&ctx->split_mode,   3, THRESH_HIGH);
+    model_init(&ctx->edge_mode,    2, THRESH_HIGH);
+    model_init(&ctx->pivot,        3, THRESH_LOW);
+    pixctx_init(&ctx->intra_pix_ctx, 8);
+    pixctx_init(&ctx->inter_pix_ctx, 2);
+    ctx->corrupted = 1;
+}
+
+void ff_mss12_codec_reset(MSS12Context *ctx)
+{
+    model_reset(&ctx->intra_region);
+    model_reset(&ctx->inter_region);
+    model_reset(&ctx->split_mode);
+    model_reset(&ctx->edge_mode);
+    model_reset(&ctx->pivot);
+    pixctx_reset(&ctx->intra_pix_ctx);
+    pixctx_reset(&ctx->inter_pix_ctx);
+
+    ctx->corrupted = 0;
+}
+
+static int decode_pivot(MSS12Context *ctx, ArithCoder *acoder, int base)
+{
+    int val, inv;
+
+    inv = acoder->get_model_sym(acoder, &ctx->edge_mode);
+    val = acoder->get_model_sym(acoder, &ctx->pivot) + 1;
+
+    if (val > 2) {
+        if ((base + 1) / 2 - 2 <= 0) {
+            ctx->corrupted = 1;
+            return 0;
+        }
+        val = acoder->get_number(acoder, (base + 1) / 2 - 2) + 3;
+    }
+
+    if (val == base) {
+        ctx->corrupted = 1;
+        return 0;
+    }
+
+    return inv ? base - val : val;
+}
+
+static int decode_region_intra(MSS12Context *ctx, ArithCoder *acoder,
+                               int x, int y, int width, int height)
+{
+    int mode;
+
+    mode = acoder->get_model_sym(acoder, &ctx->intra_region);
+
+    if (!mode) {
+        int i, pix;
+        int stride = ctx->pic_stride;
+        uint8_t *dst = ctx->pic_start + x + y * stride;
+
+        pix = decode_top_left_pixel(acoder, &ctx->intra_pix_ctx);
+        for (i = 0; i < height; i++, dst += stride)
+            memset(dst, pix, width);
+    } else {
+        return decode_region(ctx, acoder, ctx->pic_start,
+                             x, y, width, height, ctx->pic_stride,
+                             &ctx->intra_pix_ctx);
+    }
+
+    return 0;
+}
+
+static int decode_region_inter(MSS12Context *ctx, ArithCoder *acoder,
+                               int x, int y, int width, int height)
+{
+    int mode;
+
+    mode = acoder->get_model_sym(acoder, &ctx->inter_region);
+
+    if (!mode) {
+        mode = decode_top_left_pixel(acoder, &ctx->inter_pix_ctx);
+        if (mode != 0xFF) {
+            return 0;
+        } else {
+            return decode_region_intra(ctx, acoder, x, y, width, height);
+        }
+    } else {
+        if (decode_region(ctx, acoder, ctx->mask,
+                          x, y, width, height, ctx->mask_linesize,
+                          &ctx->inter_pix_ctx) < 0)
+            return -1;
+        return decode_region_masked(ctx, acoder, ctx->pic_start,
+                                    ctx->pic_stride, ctx->mask,
+                                    ctx->mask_linesize,
+                                    x, y, width, height,
+                                    &ctx->intra_pix_ctx);
+    }
+
+    return 0;
+}
+
+int ff_mss12_decode_rect(MSS12Context *ctx, ArithCoder *acoder,
+                         int x, int y, int width, int height)
+{
+    int mode, pivot;
+
+    if (ctx->corrupted)
+        return -1;
+
+    mode = acoder->get_model_sym(acoder, &ctx->split_mode);
+
+    switch (mode) {
+    case SPLIT_VERT:
+        pivot = decode_pivot(ctx, acoder, height);
+        if (ff_mss12_decode_rect(ctx, acoder, x, y, width, pivot))
+            return -1;
+        if (ff_mss12_decode_rect(ctx, acoder, x, y + pivot, width, height - pivot))
+            return -1;
+        break;
+    case SPLIT_HOR:
+        pivot = decode_pivot(ctx, acoder, width);
+        if (ff_mss12_decode_rect(ctx, acoder, x, y, pivot, height))
+            return -1;
+        if (ff_mss12_decode_rect(ctx, acoder, x + pivot, y, width - pivot, height))
+            return -1;
+        break;
+    case SPLIT_NONE:
+        if (ctx->keyframe)
+            return decode_region_intra(ctx, acoder, x, y, width, height);
+        else
+            return decode_region_inter(ctx, acoder, x, y, width, height);
+    default:
+        return -1;
+    }
+
+    return 0;
+}
+
+av_cold int ff_mss12_decode_init(AVCodecContext *avctx, int version)
+{
+    MSS12Context * const c = avctx->priv_data;
+    int i;
+
+    c->avctx = avctx;
+
+    if (avctx->extradata_size < 52 + 256 * 3) {
+        av_log(avctx, AV_LOG_ERROR, "Insufficient extradata size %d\n",
+               avctx->extradata_size);
+        return AVERROR_INVALIDDATA;
+    }
+
+    if (AV_RB32(avctx->extradata) < avctx->extradata_size) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Insufficient extradata size: expected %d got %d\n",
+               AV_RB32(avctx->extradata),
+               avctx->extradata_size);
+        return AVERROR_INVALIDDATA;
+    }
+
+    av_log(avctx, AV_LOG_DEBUG, "Encoder version %d.%d\n",
+           AV_RB32(avctx->extradata + 4), AV_RB32(avctx->extradata + 8));
+    c->free_colours     = AV_RB32(avctx->extradata + 48);
+    if ((unsigned)c->free_colours > 256) {
+        av_log(avctx, AV_LOG_ERROR,
+               "Incorrect number of changeable palette entries: %d\n",
+               c->free_colours);
+        return AVERROR_INVALIDDATA;
+    }
+    av_log(avctx, AV_LOG_DEBUG, "%d free colour(s)\n", c->free_colours);
+    avctx->coded_width  = AV_RB32(avctx->extradata + 20);
+    avctx->coded_height = AV_RB32(avctx->extradata + 24);
+
+    av_log(avctx, AV_LOG_DEBUG, "Display dimensions %dx%d\n",
+           AV_RB32(avctx->extradata + 12), AV_RB32(avctx->extradata + 16));
+    av_log(avctx, AV_LOG_DEBUG, "Coded dimensions %dx%d\n",
+           avctx->coded_width, avctx->coded_height);
+    av_log(avctx, AV_LOG_DEBUG, "%g frames per second\n",
+           av_int2float(AV_RB32(avctx->extradata + 28)));
+    av_log(avctx, AV_LOG_DEBUG, "Bitrate %d bps\n",
+           AV_RB32(avctx->extradata + 32));
+    av_log(avctx, AV_LOG_DEBUG, "Max. lead time %g ms\n",
+           av_int2float(AV_RB32(avctx->extradata + 36)));
+    av_log(avctx, AV_LOG_DEBUG, "Max. lag time %g ms\n",
+           av_int2float(AV_RB32(avctx->extradata + 40)));
+    av_log(avctx, AV_LOG_DEBUG, "Max. seek time %g ms\n",
+           av_int2float(AV_RB32(avctx->extradata + 44)));
+
+    for (i = 0; i < 256; i++)
+        c->pal[i] = AV_RB24(avctx->extradata + 52 + i * 3);
+
+    avctx->pix_fmt = PIX_FMT_PAL8;
+
+    c->mask_linesize = FFALIGN(avctx->width, 16);
+    c->mask          = av_malloc(c->mask_linesize * avctx->height);
+    if (!c->mask) {
+        av_log(avctx, AV_LOG_ERROR, "Cannot allocate mask plane\n");
+        return AVERROR(ENOMEM);
+    }
+
+    codec_init(c);
+
+    return 0;
+}
+
+av_cold int ff_mss12_decode_end(AVCodecContext *avctx)
+{
+    MSS12Context * const c = avctx->priv_data;
+
+    av_freep(&c->mask);
+
+    return 0;
+}
diff --git a/libavcodec/mss12.h b/libavcodec/mss12.h
new file mode 100644
index 0000000000..383d86c904
--- /dev/null
+++ b/libavcodec/mss12.h
@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2012 Konstantin Shishkov
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * Common header for Microsoft Screen 1 and 2
+ */
+
+#ifndef AVCODEC_MSS12_H
+#define AVCODEC_MSS12_H
+
+#include "avcodec.h"
+#include "get_bits.h"
+
+#define MODEL_MIN_SYMS    2
+#define MODEL_MAX_SYMS  256
+#define THRESH_ADAPTIVE  -1
+#define THRESH_LOW       15
+#define THRESH_HIGH      50
+
+typedef struct Model {
+    int cum_prob[MODEL_MAX_SYMS + 1];
+    int weights[MODEL_MAX_SYMS + 1];
+    int idx2sym[MODEL_MAX_SYMS + 1];
+    int sym2idx[MODEL_MAX_SYMS + 1];
+    int num_syms;
+    int thr_weight, threshold;
+} Model;
+
+typedef struct ArithCoder {
+    int low, high, value;
+    GetBitContext *gb;
+    int (*get_model_sym)(struct ArithCoder *c, Model *m);
+    int (*get_number)   (struct ArithCoder *c, int n);
+} ArithCoder;
+
+typedef struct PixContext {
+    int cache_size, num_syms;
+    uint8_t cache[12];
+    Model cache_model, full_model;
+    Model sec_models[4][8][4];
+} PixContext;
+
+typedef struct MSS12Context {
+    AVCodecContext *avctx;
+    uint8_t        *pic_start;
+    int            pic_stride;
+    uint8_t        *mask;
+    int            mask_linesize;
+    uint32_t       pal[256];
+    int            free_colours;
+    int            keyframe;
+    Model          intra_region, inter_region;
+    Model          pivot, edge_mode, split_mode;
+    PixContext     intra_pix_ctx, inter_pix_ctx;
+    int            corrupted;
+} MSS12Context;
+
+int ff_mss12_decode_rect(MSS12Context *ctx, ArithCoder *acoder,
+                         int x, int y, int width, int height);
+void ff_mss12_model_update(Model *m, int val);
+void ff_mss12_codec_reset(MSS12Context *ctx);
+av_cold int ff_mss12_decode_init(AVCodecContext *avctx, int version);
+av_cold int ff_mss12_decode_end(AVCodecContext *avctx);
+
+#endif /* AVCODEC_MSS12_H */